In a large skillet, heat oil over medium-low heat. Add the onion and sauté, stirring occasionally, until it turns soft (approximately 5 minutes). Add the garlic and cook until it becomes fragrant, about 1 minute.
Add the mushrooms and cook until mushrooms release and evaporate their liquid, roughly 10 minutes. Remove from heat to cool.
Heat an oven to 350° F.
Combine the turkey, grated potato, cooked quinoa, cooked vegetables, Dijon mustard, Worcestershire, eggs, salt, chili flakes and pepper in a large bowl. Mix just until combined, the mixture will be moist. Place the mixture into a loaf pan or shape into a loaf and place on a baking pan lined with parchment paper.
Place in the preheated oven and bake for approximately 30 minutes, remove from the oven and spread the ketchup on top of the meatloaf. Bake further for 20 minutes or until it is cooked through. Check doneness with an instant-read thermometer; it should read at least 160°F when inserted into the center.
Allow the meatloaf to cool for 10 minutes before slicing and serving.
Garnish with parsley if desired!